For example, many new investors forget or underestimate vacancy, maintenance and cap ex.

Are you looking for someone to do full-scale remodels/flips, or more just someone on call to do any necessary maintenance and repairs that come up?

If I were you, I would ask them directly why they need an NDA.Like you said, it is not common request.

Assume you can turn your $110K asset after selling costs into 3 Memphis units that each cash flow $200/month after realistic PM, cap ex/maintenance estimate, and vacancy estimate (a bigger challenge than it may seem because maintenance and cap expense do not vary that significantly base on the rent as much as the unit profile (number of bathrooms, square footage, etc.); cheaper rents have a higher percentage of the rent needed for cap ex/maintenance. 

My price is directly derived from my valuation, and these owners have mentioned that the cap ex, maintenance  and management allotments are to high(I'm using the standard %'s) which makes my offer to low.

I know that some of the replies here will be common expenses and others will be not so common.

Kyle, it's not a rocket science, just common sense accounting practices. 

Flooring, paint, holes, general maintenance, etc. 

It doesn't matter that the rents aren't showing up on you last tax return, they will just take your gross rents from your leases and subtract 25% as a vacancy / maintenance factor and then subtract the new mortgage PITI from the remaining number.

I'm really unsure if I should be opening a new bank account for rent/maintenance, if I should be creating an LLC or just use my current bank account.